Double circular barplot





This post describes how to build a special circular barplot with d3.js. Two numeric variables are available for each group of the dataset, and are facing each other on the chart. This example illustrates the distortion that bars face on this type of chart. Visit data-to-viz.com for more info.


Circular barplot section

Steps:

  • This example is pretty straight forward to build if you alreday understood the previous circular barplot with label.

  • It just adds a second Y scale oriented in the other side: from innerRadius to ~0

  • Note: here the same variable is used for the inner and the outer part. It illustrates the main caveat of circular barcharts: see how the bar size is distorted?
<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>

<!-- Function for radial charts -->
<script src="https://cdn.jsdelivr.net/gh/holtzy/D3-graph-gallery@master/LIB/d3-scale-radial.js"></script>

<!-- Create a div where the graph will take place -->
<div id="my_dataviz"></div>

<script>

// set the dimensions and margins of the graph
var margin = {top: 100, right: 0, bottom: 0, left: 0},
    width = 460 - margin.left - margin.right,
    height = 460 - margin.top - margin.bottom,
    innerRadius = 90,
    outerRadius = Math.min(width, height) / 2;   // the outerRadius goes from the middle of the SVG area to the border

// append the svg object
var svg = d3.select("#my_dataviz")
  .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + (width / 2 + margin.left) + "," + (height / 2 + margin.top) + ")");

d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/7_OneCatOneNum.csv", function(data) {

  // X scale: common for 2 data series
  var x = d3.scaleBand()
      .range([0, 2 * Math.PI])    // X axis goes from 0 to 2pi = all around the circle. If I stop at 1Pi, it will be around a half circle
      .align(0)                  // This does nothing
      .domain(data.map(function(d) { return d.Country; })); // The domain of the X axis is the list of states.

  // Y scale outer variable
  var y = d3.scaleRadial()
      .range([innerRadius, outerRadius])   // Domain will be define later.
      .domain([0, 13000]); // Domain of Y is from 0 to the max seen in the data

  // Second barplot Scales
  var ybis = d3.scaleRadial()
      .range([innerRadius, 5])   // Domain will be defined later.
      .domain([0, 13000]);

  // Add the bars
  svg.append("g")
    .selectAll("path")
    .data(data)
    .enter()
    .append("path")
      .attr("fill", "#69b3a2")
      .attr("class", "yo")
      .attr("d", d3.arc()     // imagine your doing a part of a donut plot
          .innerRadius(innerRadius)
          .outerRadius(function(d) { return y(d['Value']); })
          .startAngle(function(d) { return x(d.Country); })
          .endAngle(function(d) { return x(d.Country) + x.bandwidth(); })
          .padAngle(0.01)
          .padRadius(innerRadius))

  // Add the labels
  svg.append("g")
      .selectAll("g")
      .data(data)
      .enter()
      .append("g")
        .attr("text-anchor", function(d) { return (x(d.Country) + x.bandwidth() / 2 + Math.PI) % (2 * Math.PI) < Math.PI ? "end" : "start"; })
        .attr("transform", function(d) { return "rotate(" + ((x(d.Country) + x.bandwidth() / 2) * 180 / Math.PI - 90) + ")"+"translate(" + (y(d['Value'])+10) + ",0)"; })
      .append("text")
        .text(function(d){return(d.Country)})
        .attr("transform", function(d) { return (x(d.Country) + x.bandwidth() / 2 + Math.PI) % (2 * Math.PI) < Math.PI ? "rotate(180)" : "rotate(0)"; })
        .style("font-size", "11px")
        .attr("alignment-baseline", "middle")

  // Add the second serie
  svg.append("g")
    .selectAll("path")
    .data(data)
    .enter()
    .append("path")
      .attr("fill", "red")
      .attr("d", d3.arc()     // imagine your doing a part of a donut plot
          .innerRadius( function(d) { return ybis(0) })
          .outerRadius( function(d) { return ybis(d['Value']); })
          .startAngle(function(d) { return x(d.Country); })
          .endAngle(function(d) { return x(d.Country) + x.bandwidth(); })
          .padAngle(0.01)
          .padRadius(innerRadius))

});

</script>

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